1. Technical Field
This invention relates generally to oil and natural gas well drilling apparatus and methods of construction thereof, and more particularly to fracture plugs and to their method of construction.
2. Related Art
It is known to use fracture plugs while forming a natural gas well to temporarily close off and isolate adjacent segments of the well from one another. Upon drilling vertically extending and horizontally extending regions of the well, a furthest distal region of the horizontal region of the well is perforated via an explosion process. Then, the shale is fractured via introduction of high pressure water. The fracturing process, sometimes referred to as frac or fracing, causes the shale to fracture, thereby allowing the gas therein to be released into the well. Upon fracing the further region of the well, a fracture plug, sometimes referred more simply as frac plug, is disposed into the well to an area immediately upstream of the fraced region. As such, the fraced region is closed off from the upstream portion of the well by the frac plug, thereby preventing the natural gas from escaping past the frac plug. Then, the process of fracing is performed again in the region immediately upstream of the originally fraced region, with another frac plug then being disposed in the well to close off and isolate the second fraced region from the upstream portion of the well. Accordingly, the two fraced regions are isolated from one another and from the upstream portion of the well with the natural gas being closed off from escaping the well by the separate frac plugs. This process is continued until the entire or substantially entire horizontally extending portion of the well is fraced. Upon completing the fracing and frac plugging process, the frac plugs are then drilled out to open the full length of the horizontal section of the well to allow the natural gas to flow from the well.
The fracture plugs, as noted above, are drilled out to allow the natural gas to be harvested. Accordingly, it is desirable to provide the frac plugs with a central core that is readily penetrable by a drill for removal of the frac plug. As shown in FIG. 1, known frac plugs 1 are constructing having a single-piece structure, with a central sand core 2 fully encapsulated by a monolithic piece of overmolded, rubber that forms an outermost shell layer 3 free of joints or seams. Upon molding the outermost shell layer 3, the rubber material thereof is vulcanized. The frac plug 1 shown also has an innermost rubber layer 4 and an intermediate rubber layer 5 between the outer and inner layers 3, 4. Though these frac plugs are useful for their intended application, their manufacturing process is complex, and thus costly. This results, at least in part, due to having to properly position and maintain the central sand core 2 in a mold cavity prior to molding the outermost shell layer 3.